For many years companies have required back/rear projection booths/rooms to shown their Corporate Films, Slides and Videos to assembled audiences. Traditionally these projection booths have been purpose built, constructed from a selection of building materials, and these back projection booths have been used at exhibitions, Station Presentations and “in house” in Training rooms, Boardrooms, etc.
The requirement for the installation of Back/rear projection booths/rooms are dependant on the application and the constraints of the space available. They are therefore usually designed and built on a “one off” basis and generally comprise of a number of disparate elements combined together to form the booth. These disparate elements would normally comprise 4 walls, a ceiling and a floor, with a large hole cut in one wall, to allow the insertion of a rear projection screen, through which the projected image is seen, a projector and lens, and some electronics including an electrical power feed and a playback and sound system.
Located somewhere within the booth/room is a film, slide or Video Projector, usually mounted in a separate projector stand, sometimes directly pointing at the screen, sometimes indirectly via a mirror. Mirrors are usually installed, to provide the correct projection distance, when the depth of the room is insufficient to allow for direct projection onto the screen. The projection distance being determined by the size of the image required, together with the projection lens being used. These booths/rooms are generally square or rectangular. The projection screen surfaces are made from various translucent materials with varying tints in an attempt to improve contrast ratios sacrificing projected light as a result.
It is usual for film, slides and video to be viewed in a darkened room just like the Cinema, thereby removing the possibility of any ambient light interfering with the projected image. The darkening of the room also has the effect of increasing the perceived brightness and the contrast of the projected image because the pupil inside the eye of the viewer, enlarges, to allow more light to fall on to the retina of the eye, which increases the perceived brightness of the projected image to the viewer. Perceived brightness to the Human eye is very dependant on the overall contrast between Black and White. As a general rule the blacker the blacks, the brighter the image to the eye.
Other than the purpose built rooms described above, the market of single integrated rear projection systems is entirely confined to the small display market with vertical/upright screen diagonals up to 55″. The most common vertical/upright sizes are in the 40″-45″ screen diagonal range. However, and without exception, all these integrated projection systems are indirect projection systems and all feature vertical/upright screens, i.e. they all use varying types of optical mirrors/reflection surfaces between the projector and the vertical/upright screen surface.
There are no direct projection systems within the integrated projection display markets. All other larger, direct or indirect, rear projection systems are found in very high cost, purpose built installations only, and where proper viewing of the vertical/upright screens can only be properly viewed in low ambient light levels.
We have appreciated a number of problems with existing rear projection units.
First, inside buildings, the amount of ambient light from fixed position lighting being reflected off the front surface of the screen into the eyes of the assembled viewers, makes the projected image difficult, uncomfortable and in some instances impossible to view. Outdoors, the same problems exists to a much greater degree due to the high daylight levels of ambient light.
Second, the amount of ambient from fixed position lighting and the general ingress of external natural ambient light, in the viewing area travelling through the translucent screen into the “projection area” and which then travels around the projection area and back out with the projected image, results in “washing out” the projected image. The net result is that the image is difficult, if not impossible to view. Inside a projection unit, a certain amount of the light from the projected image is reflected off the internal side of the translucent screen back into the internal “projection area”. This additional, randomly reflected, light mixes with the incoming ambient light and travels around the projection area passing out through the screen with the image, thus increasing the “washing out” effect.
Third, vertical/upright screens, which are not centred at head height and in line with the assembled viewers eyes, create considerable additional problems due to the “off centre” viewing angles. These “off centre” viewing angles create additional bright and dark screen areas (various known as hot and cold spots etc.) because the viewers eyes are not directly in alignment with the projector and the projected image, being always offset due to the fact that the screen is in the vertical/upright plane.
Fourth, rear direct/indirect projection systems suffer from air borne atmospheric dust/pollution which causes the optics to become coated with air borne grime which causes light loss, and further, the projected light that is emitted from the optics is caused to refract in the air between the point of exit from the projection optics and the rear of the screen material. This internal air refraction downgrades the clarity of the projected image.
Lastly, in general, we have appreciated the need for a rear projection unit which does not require a purpose built room.